The disclosure relates to threaded tubular connections and the like. More particularly, the disclosure relates to an apparatus and method for joining tubular members using threaded sections in a manner that increases the thread torque capacity.
In the oil and gas production industry, pipe or other tubular sections may be connected via threaded connections, such as mating pin and box ends. The threaded connections are often subjected to large torsion forces, such as during downhole operations like drilling. The torque or yield strength of the connection is dictated by the thread profile, the material properties and the dimensions of the mating threaded components. However, due to space or other constraints in a well bore, often times the threaded connection design is limited as to the size and thread type that can be used, thereby limiting the yield strength of the connection. It is particularly problematic to achieve increased yield strength in a connection that is made up onto the threaded pin face. Sometimes it is necessary to have a connection that is stronger than what can be achieved in an existing design. Thus, it is advantageous to increase the yield or torque strength of a threaded connection.
To increase the torque capacity of a particular threaded connection, a thread locking compound (such as Loctite®) is sometimes applied to the threads. This tends to increase the friction between the mating threaded components, thus increasing the torque capacity of the overall connection. However, thread locking compounds are undesirable because the threaded connection can be very difficult to disassemble after makeup because the connection must be heated to break down the locking compound. This is a time consuming process and the high heat required to break apart the thread locking compound can damage equipment.
Other attempts to increase the torque capacity of the connection include using higher strength material for the threaded components or using a double shoulder type design. However, higher strength materials are generally more expensive and might not be available. Furthermore, even high strength materials, alone, might fail to meet the high torque requirements of drilling operations. Additionally, double shoulder type threaded connections require precise dimensional tolerances among the fixed outer pin face to outer box face interface and the fixed inner pin face to inner box face interface. Should these dimensions be imprecise, similar threaded connections may have torque strengths that are dissimilar, unpredictable, and yield little advantage over standard threaded connections.
Applying thread locking compound, changing the thread profile or changing material selection all present significant disadvantages when attempting to improve the yield strength of a threaded connection under high torsional loads. Thus, there remains a need for a threaded connection that advantageously increases the torque strength of a threaded connection, particularly while also staying within current downhole design specifications.